The interphotoreceptor matrix (IPM) is the thin layer of extracellular material occupying the subretinal space in normal vertebrate eyes. Because it is located between the neural retina and the pigment epithelium (PE), the IPM is in a strategic position to perform several important functions for the retina. No reports have yet appeared on whether the IPM is involved, for example, in retinal nutrition, retinoid transport, enzymatic digestion of shed disc material and/or retinal adhesion. The main purpose of the proposed research is to identify and investigate biochemical components of this matrix that may be required to maintain the health of the retina. We have already shown that, in addition to the small amount of glycosaminoglycans known to be present, bovine IPM contains about 8 mg protein (and glycoprotein) per eye. From gel electrophoresis, most of the matrix proteins appear to be newly synthesized products of the retina and PE. The functions of the IPM proteins are, as yet, unknown. One project is to determine whether retinoids pass through the IPM to travel to and from the retina (for incorporation into visual pigment) and the PE (for storage). The quantities of retinol and its esters in bovine IPM will be measured by thin layer and high-performance liquid chromatography, after dark and light adaptation of bovine eyes. Amounts and molecular weights of retinol-binding proteins in the matrix will be examined by gel chromatography; fractions will be analyzed by fluorescence. Another goal is to search in the IPM for the presence of hydrolytic enzymes (of PE lysosomal origin), which may begin the process of digesting shed disc packets prior to phagocytosis; methods to be employed include colorimetric and fluorometric enzyme assays in isolated IPM, and histochemistry in situ. Other research on IPM components includes examination of glycoproteins and glycosaminoglycans as possible factors in maintenance of retinal adhesion, and evaluation of the matrix as a nutritional medium. Additional aims are to study the ontogeny of IPM proteins (in the developing chick eye), to compare IPM composition in various vertebrates (cow, rabbit, human, rat, chicken), and to see whether retinal dieseases (e.g., retinal degeneration in the RCS rat) affect the matrix composition. We anticipate that the proposed investigation of the hitherto neglected IPM will increase our knowledge of how the health of the retina is maintained, and provide clues about faulty functioning in disease states.